<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        canvas{
            position: absolute;
            top: 0;
            left: 0;
        }
    </style>
    <script src="js/_canvas.js"></script>
    <script>
        window.onload = function () {
           const cvs = new Mycanvas('c1',500,500)
        };
    </script>
</head>
<body>
<canvas width="500" height="500" id="c1"></canvas>
<canvas width="500" height="500" id="c2"></canvas>
</body>
</html>